1. Field of the Invention
The present invention relates to an automatic sheet feeder adapted for use in an image forming device, such as a printer, a copier, fax machines, and a so-called multi-function machine that includes print, copy, and fax functions, or the like, and more particularly, to an apparatus to guide a printing sheet in the office machine, to set the printing sheet to be loaded in the automatic sheet feeder according to its width and size, and to prevent the printing sheet from being fed in a skewed or inclined state during a pickup operation.
2. Description of the Related Art
Generally, an office machine, for example, a printer, a copier, a facsimile machine, or the like, includes, inter alia, an automatic sheet feeder having a printing sheet cassette or a tray containing a large number of sheets, a pickup roller assembly to pick up the uppermost sheet of the sheets contained in the printing sheet tray to be fed into the printer, a printing component for printing given images or letters on the printing sheet fed by the automatic sheet feeder, and a discharging unit for discharging the printing sheet printed by the printing component from the printer.
Among these components of the office machine, the automatic sheet feeder is provided with a sheet guide for guiding the printing sheet in the printing sheet tray during the sheet feeding process so as to prevent the printing sheet from being skewed.
Referring to FIG. 1, there is illustrated a conventional automatic sheet feeder 10 having a sheet guide.
The automatic sheet feeder 10 includes a plate 11 having formed thereon a first latch part 12a having a plurality of latches with a given pitch and a guide hole 12b. The automatic sheet feeder 10 further includes a sheet-side guide 20 being slidably held to the plate 11 such that the sheet-side guide 20 slides along the guide hole 12b. A second latch part 21 (FIG. 2) of the sheet-slide guide 20 has a latch positioned in a serrated engagement with the latches of the first latch part 12a in the plate 11. The automatic sheet feeder 10 may also include a pickup roller assembly 30 mounted over the plate 11 to feed the printing sheet set by the sheet-side guide 20.
In order to release the serrated engagement between the first and second latch parts 12a, 21 to move the sheet-side guide 20, a latch-releasing handle 23 is formed at a portion of the sheet-side guide 20.
As illustrated in FIG. 3, the sheet-side guide 20 supporting an edge of the printing sheet is slidably held in the guide hole 12b of the plate 11 by a latch guide 13. The latch guide 13 is engaged with a plurality of fixing pieces 22a, 22b formed as an elastic member on a bottom of the sheet-side guide 20 to be inserted in the guide hole 12b, and fastened to a fixing member 22c formed on the bottom of the sheet-side guide 20, by a screw 26.
In operation, the serrated engagement between the first latch part 12a and the second latch part 21 is disengaged by gripping or pushing the latch-releasing handle 23, and then the sheet-side guide 20 is allowed to slide along the guide hole 12b on the plate 11 so that the guide face 24 is set against side edges of the printing sheets in order to accommodate different sizes of the sheets.
When a printing sheet is picked up and fed by the pickup roller assembly 30, the sheet-side guide 20 sets and supports a side edge of the sheet to prevent the printing sheet from being fed in a skewed or twisted state, which may be caused by the pickup friction force generated by the pickup roller assembly 30.
However, in the automatic sheet feeder 10, a gap between the fixing pieces 22a, 22b of the sheet-side guide 20 and the guide hole 12b exists due to fabrication error, tolerance, etc. The rotation-twist force generated by the pickup roller assembly 30 in a pickup operation may cause the sheet-side guide 20 to move as much as the gap, this in turn allows the printing sheet freedom of movement. When the printing sheet is allowed to move, it may still be fed in the skewed state since the side edge of the printing sheet may not conform to the guide face 24 of the sheet-side guide 20. Thus, the printing sheet may not be in the proper alignment or orientation. This may cause a paper jam, or a skewed printing, and thus causing the printing quality to deteriorate.
Moreover, the sheet-side guide 20 itself may become misaligned. This is because of the above mentioned gap and the structure of the sheet-side guide 20 where the guide face 24 extends along a length, and is supported by a single point along the guide hole 12b. When a sheet, which extends along only a portion of the guide face 24, is being fed, the pickup friction force imparted on the printing sheet by the pickup roller assembly 30 is exerted mostly on the portion of the guide face 24, with which the edge of the makes contacts with the guide. The uneven exertion of the force subjects the sheet-side guide 20 to a moment of rotation, and causes the sheet-side guide 20 to pivot about the single supporting point. This tendency for the sheet-side guide 20 to pivot becomes particularly profound when a small size paper, e.g., an envelope, a post card, or the like, is being fed since the moment of rotation becomes greater. As a result, the sheet-side guide 20 may tilt from the proper alignment, causing the printing sheet to be fed in the skewed state.
In a conventional automatic sheet feeder 10, in order to prevent the undesirable movement of the sheet-side guide 20, an upper surface 25 of the sheet-side guide 20 is made to closely contact a sidewall 15 of a recess 14 formed on the plate 11. Alternately, in another prior attempt to solve the above problem, an additional guide hole (not shown) to support the sheet-side guide 20 is provided to allow the sheet-side guide 20 to be supported along two sliding holes. However, the shortcoming associated with these prior attempts is that the sliding movement of the sheet-side guide 20 generates a surface friction between the upper surface 25 of the sheet-side guide 20 and the sidewall 15 and/or between the additional fixing pieces and the additional guide hole, making it difficult to slide the sheet-side guide 20 when adjusting the same for different sizes of the sheets. There is also an attempt to remove the surface friction by applying lubricating oil, but the lubricating oil alone cannot completely remove the frictional resistance. The lubricating oil may contaminate the printing sheet or other components of the office machine, which may be further exacerbated by the collection dust by the lubricating oil.